- for sizeof(void *) == 8 arch, this is mandatory. MHLEN is too small
already (less than 80) and there are chances for unwanted packet loss due
to m_pullup restriction.
- for other cases, the change should avoid allocating clusters in most cases
(even when you have IPv4 IPsec tunnel, or IPv6 with moderate amount of
extension header)
portmasters: if your arch chokes with the change (high memory usage or
whatever), please backout the change for your arch.
bjh21